1. Field of the Invention
The present invention relates in general to a method of producing an intraocular lens which is made of a polyimide material and has good transparency and excellent optical properties. In particular, the invention is concerned with a method of producing a one-piece type intraocular lens consisting of integrally formed optic and haptic, which method permits quantity production of such one-piece type intraocular lenses at a low cost.
2. Discussion of the Related Art
Conventionally, there are known two-piece or three-piece type intraocular lenses produced by assembling or fixing together an optical member and a support member which are prepared independently of each other. Also known are one-piece type intraocular lenses each having an optic and a haptic formed integrally with the optic. The haptic or other support member serves to hold the lens in position within the eye. At present, the one-piece type intraocular lenses are preferably used since they can be manufactured with an improved efficiency.
In fact, the known one-piece type intraocular lenses have been produced only by mechanical processing such as cutting and polishing. To form a lens having a convex surface and a planar surface as opposite lens surfaces, for example, a disc-like lens blank made of a suitable material (hereinafter referred to as "molding material") is initially embossed at its one surface with an optic and a haptic of the lens to be formed, and the optic is then cut and polished to thereby provide a suitably curved lens surface. Thereafter, with this curved surface bonded to and securely held by a suitable jig or fixture, the other surface of the lens blank is subjected to plane cutting, and remaining portions of the lens blank are then removed off. After the thus cut surface is polished, the jig is removed and a desired intraocular lens is obtained. This method, however, is disadvantageous in its extraordinary cumbersome and time-consuming process steps. Further, an undesirably large amount of the molding material is wasted for the production of the lens according to the above method, thus resulting in reduced production efficiency and increased cost for manufacturing such lenses.
Another method of producing an integrally formed intraocular lens is disclosed in U.S. Pat. No. 5,141,677, in which a sheet made of polymethylmethacrylate (PMMA) is stamped under a pressure at an elevated temperature, using a suitable die. While this method may be applied to intraocular lenses made of PMMA as a conventional IOL material, the same method is not suitable for producing intraocular lenses made of polyimide materials which are highly expected as a favorable IOL material in these years. This is because the polyimide materials have a relatively high molding temperature, and exhibit poor flowability upon fusing thereof, which results in poor formability (moldability). Further, the polyimide materials tend to be colored due to heat applied upon molding thereof, and also suffer from optical strains and other problems. Although the production efficiency should be further improved, that is, the use of relatively expensive polyimide materials should be limited, so as to obtain the intraocular lenses at a reduced cost, the above-indicated U.S. Patent does not provide any suggestions for meeting this requirement.